(1) Field of the Invention
The present invention relates to non-destructive testing and particularly to a medical diagnostic technique which requires neither invasion of the body or the use of ionizing radiation. More specifically, this invention is directed to transillumination and especially to creating a display which is indicative to the amount of absorption at each point in the object of light having a plurality of preselected different wavelengths. Accordingly, the general objects or the present invention are to provide novel and improved methods of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention has particular significance as a breast examination device and method. At the present time there is no accepted procedure, other than palpation by a physician, which may be employed for the routine screening of patients, particularly those under the age of fifty, in an effort to diagnose breast cancer. The most widely accepted current diagnostic technique comprises mammography which, because it requires the use of ionizing, i.e., X-ray, radiation, is customarily employed only subsequent to palpation having revealed an apparent abnormality.
Other non-invasive examination techniques which are available include thermography and echography. Both of these techniques have been found to be only very limited utility and thus their application has largely been to supplement information obtained through the use of mammography.
It has also been proposed to utilize transillumination, i.e., the passing of light through tissue, in order to diagnose abnormalities. Prior transillumination techniques and apparatus are disclosed in U.S. Pat. Nos. 3,127,115, 3,371,202, 3,527,932, 3,674,008, 3,711,700, 3,732,416, 3,769,963, 4,077,399, 4,212,306 and 4,286,602. Transillumination, which is also known in the art as diaphanography or diaphanoscopy, is also discussed in Russian Pat. Nos. 279,879 and 591,178 as well as the publication "Diaphanologie mammaire" by C. Gros et al. which appeared in J. Radiol Electrol., 1972, Vol. 53, No. 4, pp. 297-306 and the article "Etude diphanoscopique des alteration dystrophiques du sein" by C. Di Maggio et al which appeared in Senologia, June 1978, No. 2, pp. 69-71. The potential advantages of transillumination versus the above-mentioned other non-invasive examination techniques are discussed in detail in U.S. Pat. No. 4,286,602.
Initial efforts to employ transillumination relied upon visual observation of the light which passed through the tissue under study. These efforts were largely unsuccessful since the human eye is not sensitive to light at the frequencies which pass through human body tissue, i.e., principally wavelengths in the range of 600 to 1500 nanometers. Light having a wavelength below 600 nanometers is largely absorbed by human body tissue while light at wavelengths above 1500 nanometers is largely absorbed by water in the tissue. The difficulty in obtaining useful information by visual observation was increased by the fact that the examination had to be performed in a darkened room and it is well known that the sensitivity of the eye to light having a wavelength within the range of interest decreases in a dark environment.
The major problems incident to visual observation were overcome when infrared light sensitive film became available. However, the use of photographic techniques employing infrared film, like the use of X-rays, does not provide information in real time. Further, since the light source and tissue under examination must be manipulated in order to insure that all regions within the tissue will be seen, and if necessary or desirable seen from different viewing angles, an examination which included recording information on film required either the taking of many pictures or was very time-consuming in that the patient had to wait while the initially taken pictures were developed and viewed so that additional pictures could be taken if necessary.
A recent improvement in transillumination technology employs a TV camera which is sensitive to light in the red and near infrared regions, i.e., in the range of 600 to perhaps 1200 nanometers. The use of a TV camera permits real time imaging and provides results which are believed to be at least comparable to those achieved through mammography but without the use of ionizing radiation. Nevertheless, there is a desire to enhance the capability of presently available transillumination devices and particularly to form an image characterized by tissue differentiation, i.e., to provide output information which is indicative of the type of tissue being illuminated.